The human PPP1R9A gene encoding neurabin I is adjacent to SGCE, PEG10, and ASB4. Neurabin I (neural tissue specific F-actin-binding protein I) was originally purified from rat brain and has been characterised as a key candidate molecule in synaptic formation and function. It has also been shown that neurabin I is highly concentrated in the synapse of developed neurons and is involved in neurite formation. The deduced 1098 amino acid sequence for rat neurabin I contains an F-actin-binding domain, a PDZ domain, and coiled-coil domains. As the name indicates, the expression of the gene and protein was shown to be brain specific in adult rat tissues. The gene symbol is based on ‘‘protein phosphatase 1, regulatory (inhibitor) subunit 9A’’ because neurabin I has been shown to bind protein phosphatase I (PP1) and inhibit its activity. The PP1/ neurabin I complex has been demonstrated to regulate actin cytoskeleton dynamics. Furthermore, molecules implicated in the control of neuronal morphology, such as p70S6K and kalirin-7 (a GTP-exchange factor), have been identified to bind the PDZ domain of neurabin I. Lastly, the C-terminus of neurabin I binds the trans-Golgi protein TGN38, suggesting it is a multi-functional molecule that regulates membrane and cytoskeletal functions.